This invention is related to oligomeric light stabilizers containing an alpha-aminoacetamide ("AAMID") repeating unit and polysubstituted piperidine chain ends. The term "polysubstituted" refers specifically to a piperidine ring in which at least the N-adjacent carbon atoms in the piperidine ring are each dialkylsubstituted, or one of the 2 or 6 C atoms is shared by a spiro cycloalkylene substituent, and the other is dialkyl-substituted. Polysubstituted piperidine compounds belong to a class of compounds referred to as hindered amines which are known to be useful as ultraviolet ("UV") light stabilizers in organic materials, whether natural or synthetic, which are to be protected against degradation by UV light.
More specifically the compounds of this invention include hindered piperidine moieties, and hindered piperidine moieties are an essential constituent of a large number of UV stabilizers and antioxidants. For example, U.S. Pat. No. 3,840,494 discloses 4-piperidinol derivatives, and Nos. 3,904,581 and 3,968,078 disclose piperidine derivatives as being good stabilizers. U.S. Pat. No. 4,293,468 discloses 4-oxo-piperidines and No. 4,293,468 discloses piperidine phosphite stabilizers; Nos. 4,069,196 and 4,069,199 disclose polypiperidines as do Great Britain Nos. 1,496,635 and 1,516,779.
Though many polysubstituted piperidines have a significant level of UV-stabilization ("UV-S") activity, each has one or more serious drawbacks which makes the one less desirable from a practical and utilitarian point of view, than another having a less serious drawback. This reality dictates the unending search, even in the narrow field of piperidine-based stabilizers, for compounds with better UV-S activity, and results in discarding numerous stabilizers which do not have commercially significant activity.
The effectiveness of the polymer of this invention is deemed to be derived as much from the poly(AAMID) body of the compounds as from the hindered piperidine chain ends. The preparation of AAMID compounds has been disclosed in U.S. Pat. No. 4,310,429 and these compounds were used primarily as antioxidants, though they exhibit other desirable stabilizing properties, and are particularly for use in synthetic ester lubricants generally known as "functional fluids".
Amino-acid amides are disclosed in earlier U.S. Pat. Nos. 2,153,707 and 3,247,200; and 3,960,984 which is incorporated by reference thereto as if fully set forth herein, discloses amide oligomers as heat stabilizers for oxymethylene polymers. Still other amides useful as antioxidants are disclosed in U.S. Pat. No. 3,665,031; and more recent U.S. Pat. Nos. 4,058,523; 4,139,605; 4,239,747; 4,250,794; and 4,336,116 disclose other amides for a variety of purposes.
The key to the preparation of the compounds of this invention is the use of the specified substituents on the pyridine and the specified diamine in a "ketoform reaction" carried out without a phase transfer catalyst, as disclosed in U.S. Pat. No. 4,466,915 which is incorporated by reference thereto as if fully set forth herein. Quite unexpectedly, the reaction results in the formation of a polymer having the AAMID repeating unit, and this polymer has highly desirable UV-S properties.